Subroutines can access all of the global data in the program in which they are defined (main program). You therefore do not need to define a parameter interface if you do not want to change any data in the subroutine, or if very little data is involved.

However, if you want subroutines to perform complex operations on data without affecting the global data in the program, you should define a parameter interface through which you can pass exactly the data you need. In the interests of good programming style and encapsulation, you should always use a parameter interface, at least when the subroutine changes data.

To prevent the value of a global data object from being changed inside a subroutine, use the following statement:

LOCAL <f>.

This statement may only occur between the FORM and ENDFORM statements. With LOCAL, you can preserve the values of global data objects which cannot be hidden by a data declaration inside the subroutine.

For example, you cannot declare a table work area that is defined by the TABLES statement with another TABLES statement inside a subroutine. If you want to use the table work area locally, but preserve its contents outside the subroutine, you must use the LOCAL statement.